The present invention pertains to manual control devices. More specifically, the present invention relates to a selectively engageable manual drive apparatus for use with a normally, automatically powered driving assembly having a movable member and a stationary member.
Automatically powered driving assemblies such as actuators of the type used to control valves typically employ reciprocating movement of a member such as a piston in a suitable chamber formed by a housing. The actuator includes suitable linkage means for converting the reciprocal movement of the piston to rotational movement which is translated to the valve element through a rotatable member such as the valve stem connected to the valve element. Actuators of the type described are particularly useful with butterfly or ball valves which employ such rotating valve elements.
Cylinder-piston type actuators used for automatic actuation of valves and other various devices employ hydraulic or pneumatic power. Since these power sources may from time to time fail, it becomes not only desirable, but in many cases necessary, to provide a means to manually control or override the actuator so as to be able, for example, to open or close the valve which is attached to the actuator. While such manual override means are known, most consume excessive amounts of space, are awkward to operate and are quite expensive.